For egg producers, the egg-laying period and the breakage of eggs laid are important problems in management, and it is an important and urgent problem to keep the egg-laying period as long as possible and decrease the percentage of breakage (percentage of the number of broken eggs based on the number of all laid eggs; referred to as the same hereinafter).
An egg contains about 2 g of calcium, most of which is contained in an eggshell as calcium carbonate, and it is known that the demand of calcium for egg-laying hens is more than twice that of non-egg-laying hens [Nutritional Studies up on Poultry (Kachiku Eiyogaku), Hiroshi Morimoto, Yokendo, 1971]. Hence, various attempts of increasing the feeding amount of calcium to egg-laying hens have been made for the purpose of fortifying eggshells, and, for example, a method of allowing a feed for poultry to contain 0.5% or more of middle-chain fatty acid calcium salts having carbon atoms of 8-12 is disclosed (Official Gazette of Japanese Laid-Open Patent Publication No. 2-177865/1990).
On the other hand, in order to fortify long-chain unsaturated fatty acids such as linoleic acid and linolenic acid in eggs according to a recent health food boom, an attempt of feeding oils and fats containing these fatty acids in a large amount or these fatty acids themselves to egg-laying hens has been made.
For example, a method of compounding linseed oil, safflower oil and the like with feeds [The Japanese Journal of Zootechnical Science (Nippon Chikusangakkai no), vol. 46, No. 5, p. 251, 1975], a method of giving egg-laying hens water having an .omega.-3-type highly unsaturated fatty acid emulsified therein (Official Gazette of Japanese Laid-Open Patent Publication No. 60-105471/1985), and a method of feeding them a feed having a high content of an .alpha.-linolenic fatty acid (Official Gazette of Japanese Laid-Open Patent Publication No. 63-237745/1988) are disclosed, and it is known that by feeding these oils and fats or fatty acids can be remarkably increased the content of long-chain unsaturated fatty acids in the lipid of eggs.
On the other hand, it is known that a Maillard-type browning material formed by heating saccharide and an amino acid, and a caramel-type browning material formed by heating saccharide have an antioxidative action [e.g., Japan Agricultural Chemistry Journal (Nihon Nogeikagakukai shi), vol. 43, No. 7, p. 484, 1969; Journal of Food Science, vol. 40, No. 3, p. 460, 1975; Chemical Abstracts, vol. 98, Article No. 33211W, 1983], and in addition, it is known that a mixture of caramel, hemicellulose, xylose and lignosulfate is used as a stabilizer of ethylenediamine dihydro iodide in storing, and that a mixture of said mixture with ethylenediamine dihydro iodide at a ratio of 1:1 (by weight) is used as a feed (Specification of U.S. Pat. No. 3,733,405, 1973).
Moreover, it is conventionally known to utilize molasses for feeds for the purpose of enriching the taste of poultry (e.g., Official Gazette of Japanese Patent Publication No. 58-35066/1983).
The method of allowing a feed for poultry to contain middle-chain fatty acid calcium salts having carbon atoms of 8-12, which is described in the above prior art, does not use long-chain unsaturated fatty acid calcium salts (in the above Official Gazette of Japanese Laid-Open Patent Publication No. 2-177865/1990, page 518, from right upper column, line 7 from the bottom, to left lower column, line 2, there is clearly described that long-chain fatty acid calcium salts cannot decrease the percentage of breakage of eggs), and hence it is impossible to fortify long-chain unsaturated fatty acids such as linoleic acid and linolenic acid in the lipid of eggs by employing said method. On the other hand, according to the method mentioned above in which, in order to fortify long-chain unsaturated fatty acids such as linoleic acid and linolenic acid in the lipid of eggs, oils and fats containing these fatty acids in a large amount or these fatty acids themselves are fed, the work of feeding hens fatty acids or oils and fats is complicated, and besides the method cannot decrease the percentage of breakage of eggs. In addition, oils and fats containing a large amount of long-chain unsaturated fatty acids have a defect that they are readily oxidized and a long-chain unsaturated fatty acid calcium salt is more readily oxidized than oils and fats containing a large amount of long-chain unsaturated fatty acids, and hence it has had various problems to compound it with feeds for poultry.
Further, the above prior arts have neither example of using a long-chain unsaturated fatty acid calcium salt for the purpose of reducing .the percentage of breakage of eggs laid and fortifying a long-chain unsaturated fatty acid in the yoke of eggs laid nor example of using said calcium salt together with a molasses, a browning material formed by heating saccharide, a browning material formed by heating saccharide and amino acids or a mixture thereof mixed at an optional ratio (hereinafter they are referred to as browning materials as a whole at times), and further, it is not known at all that the egg-laying period may be extended by using them together.